Colloquium: Spintronics in graphene and other two-dimensional materials

After the first unequivocal demonstration of spin transport in graphene (Tombros et al., 2007), surprisingly at room temperature, it was quickly realized that this novel material was relevant for both fundamental spintronics and future applications. Over the decade since, exciting results have made the field of graphene spintronics blossom, and a second generation of studies has extended to new two-dimensional (2D) compounds. This Colloquium reviews recent theoretical and experimental advances on electronic spin transport in graphene and related 2D materials, focusing on emergent phenomena in van der Waals heterostructures and the new perspectives provided by them. These phenomena include proximity-enabled spin-orbit effects, the coupling of electronic spin to light, electrical tunability, and 2D magnetism.Comment: 30 pages, 12 figure

Screening and interlayer coupling in multilayer graphene field-effect transistors

With the motivation of improving the performance and reliability of aggressively scaled nano-patterned graphene field-effect transistors, we present the first systematic experimental study on charge and current distribution in multilayer graphene field-effect transistors. We find a very particular thickness dependence for Ion, Ioff, and the Ion/Ioff ratio, and propose a resistor network model including screening and interlayer coupling to explain the experimental findings. In particular, our model does not invoke modification of the linear energy-band structure of graphene for the multilayer case. Noise reduction in nano-scale few-layer graphene transistors is experimentally demonstrated and can be understood within this model as well.Comment: 13 pages, 4 figures, 20 reference

Observation of the Fractional Quantum Hall Effect in Graphene

When electrons are confined in two dimensions and subjected to strong magnetic fields, the Coulomb interactions between them become dominant and can lead to novel states of matter such as fractional quantum Hall liquids. In these liquids electrons linked to magnetic flux quanta form complex composite quasipartices, which are manifested in the quantization of the Hall conductivity as rational fractions of the conductance quantum. The recent experimental discovery of an anomalous integer quantum Hall effect in graphene has opened up a new avenue in the study of correlated 2D electronic systems, in which the interacting electron wavefunctions are those of massless chiral fermions. However, due to the prevailing disorder, graphene has thus far exhibited only weak signatures of correlated electron phenomena, despite concerted experimental efforts and intense theoretical interest. Here, we report the observation of the fractional quantum Hall effect in ultraclean suspended graphene, supporting the existence of strongly correlated electron states in the presence of a magnetic field. In addition, at low carrier density graphene becomes an insulator with an energy gap tunable by magnetic field. These newly discovered quantum states offer the opportunity to study a new state of matter of strongly correlated Dirac fermions in the presence of large magnetic fields

Tunable stress and controlled thickness modification in graphene by annealing

Graphene has many unique properties which make it an attractive material for fundamental study as well as for potential applications. In this paper, we report the first experimental study of process-induced defects and stress in graphene using Raman spectroscopy and imaging. While defects lead to the observation of defect-related Raman bands, stress causes shift in phonon frequency. A compressive stress (as high as 2.1 GPa) was induced in graphene by depositing a 5 nm SiO2 followed by annealing, whereas a tensile stress (~ 0.7 GPa) was obtained by depositing a thin silicon capping layer. In the former case, both the magnitude of the compressive stress and number of graphene layers can be controlled or modified by the annealing temperature. As both the stress and thickness affect the physical properties of graphene, this study may open up the possibility of utilizing thickness and stress engineering to improve the performance of graphene-based devices. Local heating techniques may be used to either induce the stress or reduce the thickness selectively.Comment: 19 pages, 7 figures, accepted by ACS nan

On reconstruction of surfaces from their apparent contours and the stationary phase observations

The University of AizuShape Modeling International 1999 - International Conference on Shape Modeling and Applications, SMI 1999 -- 1 March 1999 through 4 March 1999 -- Aizu-Wakamatsu -- 99693The main results of the paper concern a classical problem: if two surfaces in the Euclidean space have congruent projections on any plane, how different can they be? We consider the apparent contours of the smooth hypersurfaces as the projection data and formulate some sufficient conditions of coincidence of the shapes of two hypersurfaces, if the shapes of their apparent contours on any 2-dimensional plane coincide. We also obtain new results on reconstruction of smooth surfaces from observations of the wavefronts generated by these surfaces. © 1999 IEEE

Detection of latent tuberculosis infection in rheumatologic diseases before anti-TNF? therapy: Tuberculin skin test versus IFN-? assay

PubMedID: 22095393We aimed to evaluate tuberculin skin test (TST) and interferon-gamma (IFN-?) test results for latent tuberculosis infection (LTBI) in patients with rheumatologic diseases prior to anti-TNF? therapy. Ninety patients were evaluated in the study at the Departments of Chest Diseases and Rheumatology for anti-TNF? therapy for their rheumatologic diseases. Tuberculin skin test was performed (Mantoux method) and peripheral blood samples were collected for IFN-? assay (QuantiFeron TB-Gold In Tube) before the anti-TNF? therapy. Of 90 patients, TST positivity was detected in 56 (62.2%) patients, while IFN-? positivity was detected in 34 (37.8%) patients. Among 56 TST positive patients, IFN-? positivity was detected in 24 (42.9%) patients, and among 34 TST negative patients, IFN-? positivity was detected in 10 (29.4%) patients. There was no significant agreement between TST and IFN-? assay results (Kappa = 0.12, P = 0.2). Forty-three (47.8%) patients were using immunosuppressive drugs owing to their rheumatologic diseases. In this group, TST and IFN-? positivity is significantly lower than in those who did not receive immunosuppressive treatment (P<0.05). We conclude that the IFN-? assay may not be preferred to TST as a diagnostic test in patients with rheumatologic diseases prior to anti-TNF? treatment. © Springer-Verlag 2011